A Hydra-enabled GPU path tracer that supports MaterialX.

gatling

1965 Ford Mustang Fastback from Wire Wheels Club, rendered in Gatling.

About

This is my toy path tracer I work on in my free time.

It is exposed as a Hydra render delegate and comes with a standalone that accepts Universal Scene Description (USD) files [Elkoura et al. 2019]. Both UsdPreviewSurface and MaterialX [Smythe et al. 2019] material network nodes are supported.

Gatling features a BVH builder with binned SAH [Wald 2007], spatial splits [Stich et al. 2009], SAH-preserving widening to nodes of 8 childs, compression, and an efficient traversal kernel [Ylitie et al. 2017]. Complex BSDFs like the Autodesk Standard Surface and the Disney BRDF are supported and importance sampled.

Build

The following is required:

• CMake 3.11+
• C11 compiler and C++14 compiler
• Vulkan SDK
• USD 21.08 with MaterialX support
• MDL SDK 2021.0.1 binaries

Do a recursive clone of the repository and set up a build folder:

git clone https://github.com/pablode/gatling --recursive
mkdir gatling/build && cd gatling/build

Pass following parameters in the CMake generation phase:

cmake .. -Wno-dev \
         -DUSD_ROOT=
   
     \
         -DMDL_ROOT=
    
      \
         -DCMAKE_INSTALL_PREFIX=
     
      /plugin/usd
         -DCMAKE_BUILD_TYPE=Release

     
    
   

Note: If you're using MSVC, be sure to select a 64-bit generator.

Build the relevant targets and install the Hydra delegate to the USD plugin folder:

cmake --build . -j8 --target hdGatling gatling --config Release
cmake --install . --component hdGatling

DXC

On Windows, Microsoft's DirectX Shader Compiler (DXC) can be used instead of Khronos's glslang. This allows for validation of the generated HLSL shader.

Download the DXC June 2021 binaries and set -DDXC_ROOT in the CMake generation phase to point to the unpacked folder. You can switch between both shader compilers using the -DGATLING_USE_DXC option.

Usage

Gatling can be used by every application which supports Hydra, either natively or through a plugin.

cekuhnen's Coffee Maker (CC-BY), slightly modified, rendered using Gatling inside Pixar's usdview tool.

A headless standalone is provided that accepts a USD file (.usd, .usda, .usdc, .usdz) as input. Make sure that there is a polygonal light source in the scene.

./bin/gatling 
   
     render.png \
    --image-width 1200 \
    --image-height 1200 \
    --spp 1024 \
    --max-bounces 8

   

Note: Disable the system's GPU watchdog or set an appropriate timeout value.

Outlook

Basic texturing is the next important feature. After that, support for MDL materials will be considered.

Further Reading

Smythe et al. 2019

Doug Smythe, Jonathan Stone, Davide Pesare, Henrik Edström. 2019. MaterialX: An Open Standard for Network-Based CG Object Looks. ASWF Open Source Day SIGGRAPH 2019. Retrieved October 25, 2021 from https://www.materialx.org/assets/MaterialX_Sig2019_BOF_slides.pdf.

Elkoura et al. 2019

George Elkoura, Sebastian Grassia, Sunya Boonyatera, Alex Mohr, Pol Jeremias-Vila, and Matt Kuruc. 2019. A deep dive into universal scene description and hydra. In ACM SIGGRAPH 2019 Courses (SIGGRAPH '19). Association for Computing Machinery, New York, NY, USA, Article 1, 1–48. DOI:10.1145/3305366.3328033

Ylitie et al. 2017

Henri Ylitie, Tero Karras, and Samuli Laine. 2017. Efficient incoherent ray traversal on GPUs through compressed wide BVHs. In Proceedings of High Performance Graphics (HPG ’17). Association for Computing Machinery, New York, NY, USA, Article 4, 1–13. DOI:10.1145/3105762.3105773

Stich et al. 2009

Stich, Martin & Friedrich, Heiko & Dietrich, Andreas. 2009. Spatial splits in bounding volume hierarchies. In Proceedings of the Conference on High Performance Graphics 2009 (HPG ’09). Association for Computing Machinery, New York, NY, USA, 7–13. DOI:10.1145/1572769.1572771

Wald 2007

Ingo Wald. 2007. On fast Construction of SAH-based Bounding Volume Hierarchies. In Proceedings of the 2007 IEEE Symposium on Interactive Ray Tracing (RT '07). IEEE Computer Society, USA, 33–40. DOI:10.1109/RT.2007.4342588

License

    Copyright (C) 2021 Pablo Delgado Krämer

    This program is free software: you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation, either version 3 of the License, or
    (at your option) any later version.

    This program is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
    GNU General Public License for more details.

    You should have received a copy of the GNU General Public License
    along with this program. If not, see 
   .